US 20060070547 A1
An electronic safety and arming unit comprises a micro electromechanical system (MEMS) shutter device. The shutter (18) is suspended by thin lightweight arms and hinges, all formed by silicon processing of SOI substrates and includes holding latches for holding the shutter (18) in the closed position. The holding latches may be released by an electrothermal actuator. The shutter (18) separates an initiator section from an explosive train (6) of munitions such as shells, thereby providing safety until the shell is fired and away from its start point. After firing, the shutter (18) is opened ready for the main explosive to be detonated by the initiator (3). The shutter (18) may be suspended by a compliant displacement multiplier and may include an electrothermal actuator such as an electrically heatable bent beam. Heating of the beam causes movement of a shutter blade from a shut condition covering a firing aperture to an open condition. Alternatively the shutter (18) may operate by inertial centrifugal forces generated by a spinning munition. The shutter (18) may include latches for retaining the shutter in its open position.
1. A miniature electronic safety and arming unit fabricated using micro electromechanical system technology, arranged for use between an explosive train and an initiator section of munitions comprising:
a suspended shutter suspended above and covering a firing aperture in a closed position;
at least one hold latch arranged to prevent movement of the shutter until receipt of an electrical signal;
the shutter and hold latch being arranged so that receipt of an electrical signal causes release of the at least one latch and allows movement of the shutter away from the firing aperture prior to operation of the initiator and detonation of the explosive train.
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The invention relates to an electronic safety and arming unit (ESAU) in which a safety mechanism is arranged between an initiator and an explosive section of a munition or rocket and the like.
Conventionally, munitions include a safety mechanism to prevent premature detonation of explosive material within the munitions during routine handling when loading into guns or launch tubes etc. as well as during the initial flight. Several known designs use clockwork or macro scale electromechanical safety systems.
One problem with prior art is related to size. Increasing demands for space in the fuse envelope for increased functionality mean that the space available for safety mechanisms is at a premium. Reducing the size of such a safety mechanism is therefore a priority.
One known arrangement suitable for miniaturisation uses sliding shutters as the safety mechanism to isolate an initiator section from the explosive train in munitions. This has problems with stiction occurring between contacting, movable parts. Assembling miniaturised sliders into guiding frames is also difficult.
The above problems are reduced, according to this invention, by the use of a suspended micro electromechanical system (MEMS) shutter device.
According to this invention, an electronic safety and arming unit arranged for use between an explosive train and an initiator section of munitions comprises:
a suspended micro electromechanical system shutter suspended resiliently above and covering a firing aperture in a closed position;
at least one hold latch arranged to prevent movement of the shutter until receipt of at least one electrical signal;
the shutter and at least one hold latch being arranged so that receipt of at least one electrical signal causes release of the at least one latch and allows movement of the shutter away from the firing aperture prior to operation of the initiator and detonation of the explosive train.
The unit may include an initiator having a flyer capable of being propelled through the firing aperture to the explosive train.
The initiator section may include an electronic foil initiator (EFI), a semiconductor bridge (SCB), a reactive bridge or a separate propellant charge and flyer.
A low voltage electrical micro heater may be included for initiation of a propellant charge.
The shutter may be attached to a compliant displacement multiplier and actuation arrangement so that receipt of an electrical signal causes movement of the shutter away from the firing aperture to allow operation of the initiator and detonation of the explosive train. Such actuation is advantageous in that it allows application of the device to unspun projectiles.
The hold latches may be controlled independent of one another so that the shutter is held closed until all latches are released. Each such release may be by operation of further electrothermally actuated devices such as bent beams. Each of the hold latches may be controlled from independent signals from independent environmental sensors, each sensor responding to a different aspect of the environment.
The compliant displacement multiplier may be a combination of electrothermal actuators, compliant hinges and armatures.
The shutter may be attached to a compliant support so that inertial centrifugal forces cause movement of the shutter away from the firing aperture to allow operation of the initiator and detonation of the explosive train.
The shutter may be a single component, or a double component with each covering about half of the firing aperture.
The electrothermal actuator may be a bent beam that deflects upon being heated, or a straight beam that extends upon heating to deflect a secondary beam.
The shutter, when in its closed position, is made robust enough to prevent the flyer from initiating the explosive train.
The shutter may further include a latch arrangement to hold the shutter in its open position after operation of the,actuation means. In the case of electrothermal actuation, this allows the shutter to remain open without a requirement for power.
In an electrothermally actuated device, the holding latch or latches may be used to allow storage of mechanical strain energy within the compliant hinge and leverage arrangement during activation of the electrothermal actuator. Such energy storage allows the shutter to open more rapidly and engage the latch more reliably to remain open.
In order to allow the shutter to survive the environment under which it must operate, the out of plane movement of the shutter may be constrained by a fixed substrate layer below, and a fixed capping layer above. Such an arrangement may be provided by known wafer scale packaging techniques. The in-plane movement of the shutter may be also be constrained by fixed supports and the at least one latch while the device is held in its closed position. When the shutter is in the open position its in-plane movement may be constrained by fixed supports and a further latch arrangement.
For some applications, two shutters may be employed in series and formed on a single wafer by replicating steps used in forming the first shutter to form the second shutter.
The shutter may also be used in other safety critical situations such as vehicle airbags, fire extinguishers etc.
Embodiments of the invention, given by way of example only, will now be described with reference to the accompanying drawing in which:
The flyer 16 is freely slidable along the bores 15, 19 but is restrained from initiating the explosive train 6 by the shutter 18 in its closed position. When the heater 11 is operated it causes the initiator explosive 13 to detonate or deflagrate thereby generating gas at a high pressure and propelling the flyer 16 towards the explosive train 6.
Alternatively the flyer may be formed during detonation or deflagration of the propellant 13 by tearing a planar layer around the edges of the bore to form a disc shaped flyer.
Alternatively a semiconducting bridge (SCB) device may be used to provide motive force for the flyer 16 in place of the electrical heater element 11 and initiator explosive 13. In this case electrical power would be used to vaporise an SCB element generating gas at high pressure and propelling the flyer towards the explosive train.
Alternatively an electronic foil initiator (EFI) device may be used to provide motive force for the flyer 16 in place of the electrical heater element 11 and initiator explosive 13. In this case electrical power would be used to vaporise a metallic element generating gas at high pressure and propelling the flyer towards the explosive train.
Alternatively a reactive bridge device may be used to provide motive force for the flyer 16 in place of the electrical heater element 11 and initiator explosive 13. In this case a combination of electrical power and chemical reaction energy would be used to vaporise a reactive element generating gas at high pressure and propelling the flyer towards the explosive train.
The shutter 18, in its closed position is capable of dissipating sufficient energy from the flyer 16 to prevent initiation of the explosive train to provide a safety condition should the initiator be fired accidentally. When the shutter 18 is caused to open, upon deflagration or detonation of the initiator explosive 13, the flyer 16 travels at high speed along the bores 15, 19 to impact on and detonate the explosive train 6.
The shape and operation of one example of shutter is shown in
Holding latches 37 (
As shown more clearly in
Operation of the shutter is as follows: The blades 21, 22 start in close proximity with one another and with the holding latches 37 in a holding condition; this is the shutter closed condition. An electric current is applied to the bent beam 34 causing its extension and bending. Such bending applies force to the hinge levers 29, 30 and 31, 32 trying to separate the blades 21, 22 which remain together under the retaining action of the holding latches 37. The second thermal beam 44 is then heated by an electric current causing bending of the beam 44 and release of the holding latches 37. As a result, the blades move apart quickly under the stored forces in the hinge levers 29, 30, and 31, 32 plus the continuing bending of the thermal beam 34. The effect is to force the blades 21, 22 apart until they engage the latches 49, 50 which hold them against returning to a closed position.
After such an opening, the initiator 13 may be ignited forcing the flyer 16 at high speed through the open shutter 18 into impact with the explosive train 6 and its resultant detonation.
The shutter may take other forms and shapes. All such variants have the common feature of a one or more piece shutter blade suspended by thin arms, levers or springs, with movement controlled by the effect of an electrical signal.
Other form of the shutter actuation means may derive motive force from the inertial centrifugal acceleration of components within a spun shell. For example the shutter of
Another example of a centrifugal acceleration actuated shutter mechanism is shown in
The blade 55 also carries two further spurs 69, 70 arranged to be retained by two hooks 71, 72 to hold the blade in its open condition against a stop 73.
When the munition 1 is fired and is clear from the launch area and spinning freely, a current may be applied to the bent beam 64. The bent beam 64 applies force to the compliant arm 63 and lever 65 arrangement which moves the hook 61 free of the spur 60. The shutter 55 is then free to move under inertial force until it meets the stop 73 and engages the latches 71, 72 which hold the shutter 55 against returning to a closed position.
The devices of FIGS. 2 to 9 may be made by the SOI processing steps shown in
The silicon on insulator process (SOI) process is started as in
The movable MEMS components of e.g.
As noted above, a typical thickness for the MEMS movable components of